Electrostatic transfer apparatus

ABSTRACT

An electrically biased transfer drum for use as a transfer mechanism in an electrostatic reproduction machine and having gripping devices for maintaining a sheet of paper on the drum during one or multiple transfer operations and other means for effecting stripout of the sheet.

United States Patent Michael J. Langdon Webster;

Alan F. McCarroll, Rochester, both of N.Y. 830,381

June 4, 1969 Oct. 12, 1971 Xerox Corporation Rochester, N.Y.

[72] Inventors [21 Appl. No. [22] Filed [45] Patented [73] Assignee [54]ELECTROSTATIC TRANSFER APPARATUS 5 Claims, 7 Drawing Figs.

[52] US. Cl. 355/4, 101/409, 101/177, 101/246 [51] Int. Cl G03g 15/16[50] Field of Search... 355/4- [56] References Cited UNITED STATESPATENTS 2,118,238 5/1938 Smith 101/177 2,865,289 12/1958 Fowlie et a1.101/409 3,520,603 7/1970 Gnage 355/4 Primary ExaminerSamuel S. MatthewsAssistant ExaminerE. M. Bero Attorneys-Norman E. Schrader, James J.Ralabate and Bernard A. Chiama ABSTRACT: An electrically biased transferdrum for use as a transfer mechanism in an electrostatic reproductionmachine and having gripping devices for maintaining a sheet of paper onthe drum during one or multiple transfer operations and other means forefiecting stripout of the sheet.

PATENTEDum 12 Ian 6 1 2 SHEET 10F 4 INVENTOR. MICHAEL J. LANGDON ALAN FfMC CARROLL ATTORNEY PATENTEDUET 12 Ian SHEET 30F 4 1 ELECTROSTATICTRANSFER APPARATUS This invention relates to an electrostatic printingmachine and in particular to a transfer mechanism for use in supportinga sheet of transfer material during the transfer of developed images inmultiple-image-recirculating programming.

With the advent of electrostatic color reproduction involving the use ofprocessing components which will produce a series of electrostaticimages of an original wherein each image is representative of aparticular color in the original and there is the need to superimposecorresponding series of developed images upon a sheet of transfermaterial, it is necessary that the images being superimposed beaccomplished with extreme accuracy of registration. In addition, forhigh-speed automatic machine operation, and for flexibility in the eventthat one or more images of a series is possible, it is necessary thatthe transfer mechanism be adapted for programming for single transfer aswell as multiple superimposed transfers.

Therefore, it is a principal object of the present invention toincorporate a transfer mechanism in an electrostatic printing machinewhich will render the machine capable of effecting one or more transfersof developed images upon a sheet of transfer material.

Another object of the invention is to utilize registration devices andsheet-edge-gripping devices in a transfer mechanism for accuratelypositioning the sheet to insure that successiveimages being transferredwill be registered with a previously transferred image.

Another object of the invention is to control and effect theregistration, supporting and stripout of a sheet of transfer material inaccordance with desired requirements.

The foregoing objects are acquired by a transfer drum serving as abiased electrode which is arranged to support a sheet of paper, and tomove the same in recirculating fashion into contact with aphotoconductive surface bearing a developed image. Registration devicesare mounted with the drum along with control mechanisms for controllingthe actuation of the device in timed sequence relative to developedimages moving into contact with the drum.

For a better understanding of the invention as well as other objects andfurther features thereof, reference is had to the following detaileddescription of the invention to be read in conjunction with theaccompanying drawings wherein:

FIG. I is a schematic view of a reproduction machine showing variouselectrostatic processing components;

FIG. 2 is an enlarged view with parts broken away of the transfer drumutilized in the present invention in one condition of operation;

FIG. 3 is a longitudinal cross-sectional view of the transfer drum andsupporting structure;

FIG. 4'is a cross-sectional view of the drum showing some parts inanother condition of operation;

FIG. 5 is a cross-sectional view of the drum showing registration of asheet of transfer material;

FIG. 6 is a cross-sectional view of the drum showing the sheet-grippingmechanism in a gripping condition; and

FIG. 7 is a cross section of a detail of the drum just prior to stripoutof the sheet.

For a general understanding of the illustrated copier/reproductionmachine, in which the invention may be incorporated, reference is had toFIG. 1 inwhich the various components for the machine are schematicallyillustrated. As in all electrostatic systems as well as a xerographicmachine of the type illustrated, a light image of a document to bereproduced is projected onto the sensitized surface of a xerographicplate to form an electrostatic latent image thereon. Thereafter, thelatent image is developed to form a xerographic powder image,corresponding to the latent image on the plate surface. The powder imageis then electrostatically transferred to a support surface to which itmay be fixed by a fusing device whereby the powder image is causedpermanently to adhere to the support surface.

In the illustrated machine, an original D to be copied is placed upon atransparent support platen fixedly arranged relative to an illuminationlamp assembly 10 positioned at the upper end of the machine as viewed inFIG. 1. While upon the platen, a programming system for the machineintroduces a lamp control circuit to cause successive energization ofthe lamps in the lamp assembly 10 for impinging light rays upon theoriginal thereby producing image rays which when acted upon byseparation filters correspond to the color informational areas on theoriginal. The image rays are projected by means of an optical lenssystem II for exposing the photosensitive surface of a xerographic plateat the exposure section A, the plate being in the form of a flexiblephotoconductive belt 12 arranged on a belt assembly generally indicatedby the reverence numeral 13.

The photoconductive belt assembly 13 may be mounted upon the frame ofthe machine and is adapted. to drive the selenium belt 12 at a constantrate in the direction of the arrow as shown in FIG. 1. During thismovement of the belt, the light-imaging rays of an original aresuccessively flashed full frame upon the surface of the belt. The beltstructure utilized comprises a layer of photoconductive insulatingmaterial such as selenium on a conductive backing that is sensitizedprior to exposure by means of a suitable charging corona generatordevice 14.

The flash exposure of the belt surface to the light image discharges thephotoconductive layer in the areas struck by light, whereby thereremains on the belt an electrostatic latent image for each exposure,each being in image configuration corresponding to the light imageprojected from the original D on the supporting platen through thecorresponding sepai'ation filters. As the belt surface continues itsmovement, the latent electrostatic images pass through a developingstation B at which there is positioned a developer assembly generallyindicated by the reference numeral 15 and where the belt is maintainedin a fiat condition. The developer assembly '15 comprises a plurality ofdeveloping devices l6, l7, l8 and 19 each of which contains a differentcolor-developing material to provide individual development of theelectrostatic images. The successively developed electrostatic imagesare transported by the belt to a transfer station C whereat a sheet ofcopy paper is moved at a speed in synchronism with the moving belt inorder to accomplish transfer of the developed images. There is providedat this station a sheet transport mechanism inthe form of a transferdrum 20 adapted to support a sheet of paper and to carry the same into,image transfer relationship with the belt 12 once for each imagetransfer operation. A sheet of paper S from a paper-handling mechanism,generally indicated by the reference numeral 21 is transported intoposition upon the drum 20 where it is supported during the imagetransfer function. The transfer of the developed image from the seleniumbelt surface to sheet material is effected by means of an electricalbias of the op posite polarity as the triboelectric charge on thedeveloping particles utilized in image development being applied to thetransfer drum 20 at the point of contact between the sheet and seleniumbelt as the sheet passes the transfer station C. a

After the sheet is stripped from the transfer drum 20, it is conveyed byconveyor 22 into a fuser assembly generally indicated by the referencenumeral 23 wherein the developed and transferred powder image on thesheet material is permanently affixed thereto. After fusing, thefinished copy is white-light-exposed images is moved out of thedevelopment.

station B and carried to the transfer station C. In this station, thebelt 12 is carried around a roller 70 which forms one of the threerollers of the belt assembly 13. Transfer occurs at the line on the belt12 resulting when the transfer drum 20, which serves as a biasedelectrode, is in contactwith the adjacent surface thereof as it is movedabout the roller 70.

The transfer drum is normally held away from the selenium belt 12 bymeans of a spring retaining force and upon a control signal from theprogramming system for the machine, will energize a solenoid forovercoming the spring force and to force the drum against the belt. Inthis manner, the operation of the transfer drum is fail-safe; that is,in the event of power failure or machine malfunctions, the drum will benormally moved into position of safety relative to the more delicatestructure of the selenium belt.

The drum 20 comprises a metallic cylinder mounted on two independentlyswinging arms and having an electrically conductive rubber blanket fixedtherearound and connected to a suitable source of electrical current forimage transfer purposes. As shown in FIGS. 2 and 3, a rubber-coatingblanket 71 is applied to a metallic cylinder 72 and is preferably madeof rubber having a resiliency such that with light pressure beingapplied thereto while in contact with the belt 12, there will be a veryslight flattening of or indentation into the rubber for enhancing imagetransfer.

One end of the metal cylinder 72 is closed by an end cap 73 having adrive shaft 74 mounted centrally thereof. The other end of the cylinder72 is also closed by a cap 75 which includes a centrally positionedhollow shaft 76. Means are pro vided for supporting the drum 20 by wayof its supporting shafts 74, 76, which will pennit movement of the druminto its two controlling positions. For this goal, the shaft 74 issuitably joumaled on one end of an arm 77 which is rotatably supportedat its other end on a shaft 78 secured to the frame 80 of the machinewith its axis parallel to the axis of the drum. Similarly, the shaft 76extends through and is joumaled on one end of an arm 81 which is similarto the arm 77 and which is also joumaled upon the shaft 78. The machineframe 80 is provided with vertically extending plates 82 for supportinga shaft 83 in a position parallel to the axis of the drum and the shaft78 and to one side of one edge of each of the arms 77, 81.

At each end of the shaft 83 there is formed a cam 85, only one of whichis shown in the drawings, and at one end of the shaft adjacent the camthere is also provided an integral lever 86. Both earns 85 are adaptedto engage the adjacent edges 87 of the arms 77, 81 for forcing thesearms to rotate about their common shaft 78 during slight rotation of theshaft 83. With the cams 85 having slight camming surfaces, this rockingmovement of the arms is slight, being sufiicient to disengage contactbetween he roller 20 and the belt 12. A coil spring 88 is held intension between one end of the lever 86 and the machine frame 80 fornormally tending to rotate the earns 85 against the arms in a directionto force the drum 20 away from the belt 12 (clockwise rotation of thearm 77, 81 in FIG. 2).

in order to overcome the spring force of spring 88, and to enable thedrum 20 to contact the belt 12 for the image transfer function, there isprovided a solenoid SOL-2 for rotating the shaft 83 in a directionopposite that produced by the spring 88. The solenoid SOL-2 is securedto the machine frame 80 and includes a plunger 90 pivotally connected toa link arm 91 secured to the shaft 83. As shown in FIG. 4, the link arm91 is on the other side of the shaft 83 from the lever 86 so that uponenergization of solenoid SOL-2, which results in the pull-in drivemotion of the plunger 90, will overcome the spring force and causerotation of the shaft 83 in a direction opposed to the spring action.This energization in effect will cause the arms 81, 77 to rotate in acounterclockwise direction and allow the drum 20 to engage the belt 12.

The transfer drum 20, in serving as an image transfer arrangement, iscapable of registering and supporting a sheet of transfer material foreither one transfer cycle or for recirculating the sheet through aplurality of transfer cycles. As previously described, the original D isexposed three times in order to produce a series of three latentelectrostatic images each of which is developed in sequence and madeready for transfer.

In order to make a single color reproduction of the original, the threedeveloped images are transferred individually and to the same sheet oftransfer material.

In order to effect precise registration and positioning of sheets oftransfer material upon the drum 20, there is provided a plurality ofregistration elements 95 mounted within and for movement radially of thedrum. To permit registration, the elements extend through openings 96formed in the periphery of the drum surface, the openings being in aline parallel to the axis of the drum. Each of the elements 95 has aflat rectangular configuration and is fonned with a outward-extendingprojection 97 which is movable radially with the elements from aposition within the periphery surface of the drum to two positionsslightly outwardly of the periphery of the drum. When in use, theleading edge of a sheet S engages the elements 95 immediately outwardlyof the projections 97 upon which the edge will be held duringrecirculation of the sheet (see FIG. 5).

Radial movement of the elements 95 is provided by means of a shaft 98mounted for rotation within the drum working in conjunction with driverods 100 secured to the shaft and which are adapted to be slidably heldwithin apertures 101 formed at the innermost ends of the element. Theshaft 98 is supported and joumaled upon the inner surface of thecylinder 72 by means of bearing blocks 102, and upon rotation of theshaft 98 the rods 100 will be swung therewith for causing the elements95 to move outwardly or inwardly as the case may be, relative to theaxis of the drum 20. In operation, the elements 95 are adapted to assumethree positions: the first, when no sheet is being transported, theelements occupy their innermost position, the second in a slightlyoutward position so that the projections 97 are positioned slightly awayfrom the peripheral surface of the drum when a sheet has been registeredas shown in FIG. 5 and third, with the projections 97 at a slightlygreater distance from the periphery so as to move the leading edge ofthe sheet away from the drum periphery just prior to stripout of thesheet as shown in FIG. 6.

Operating in close conjunction with the registration elements 95 are aplurality of gripper fingers 105 which are secured to the shaft 98 bymeans of clamps 106 and which extend through openings 107 formed in theperiphery of the drum 20 in alignment with the openings 96 for theelements 95. As shown in FIG. 6, when viewing the drum 20 axially, thefingers 105 and the elements 95 are in alignment parallel to the axis ofthe drum. A spring 108 is held in tension between an anchor fixed to theinterior of the cylinder 72 and a link 109 secured to the shaft 98 fornormally biasing the elements 95 in their retracted or innermostposition and the fingers 105 in their paper-clamping position.

One end of the shaft 98 has a'crank arm 110 secured thereto adjacent toand inwardly of the end cap 75. A connecting rod 111 secured to one endof the am 110 projects through an opening 112 in the end cap 75, and isconnected externally of the drum to a linkage system which will controlthe operation of the registration elements 95 and the gripper fingers105.

The linkage system comprises a link member 113 pivotally mounted at oneend by a pivot pin 114 to the upper end of the arm 81; a second linkmember 115 pivotally connected at one end to the free end of the linkmember 113; and a third link member 116 pivotally connected at one endto the free end of the link member 115. The link member 116 is securedintermediate its ends to a shaft 117 of a rotary solenoid SOL3 mountedon the arm 81. When the solenoid SOL-3 is not energized, a spring (notshown) built into the solenoid will normally maintain the linkage in theposition shown in FIG. 3. When the solenoid is energized, clockwiserotation is imparted to the link 116 thereby forcing the link member 115downwardly and to the left causing clockwise rotation of the link 113about the pivot pin 114. This position of the linkage system is shown atFIG. 2, with the solenoid energized. In effeet, the pivot pin 114 andthe solenoid shaft 117 supports the linkage system.

A cam lobe in the form of a detent 120 is formed on the inner edge ofthe link 113, and similarly the inner edge of the link 1 16 is formedwith a cam lobe in the form of a detent 121. Actually, the inner edgesof the links 113, 116 are camming surfaces as will be presentlydescribed, and the detent curves mainly control the camming effect ofthese edges. Each of the detents 120, 121 is adapted to cooperate forspecific operation with a cam follower 122 in the form of a bearing racesecured to the exterior end of the rod 111. During rotation of thetransfer drum 20, the connecting rod 111 revolves about the axis of thedrum since the shaft 98 and the opening 1 12 for the rod 111 move in arevolving motion about the axis. As the rod 111 revolves, it carries thecam follower 122 therewith in a circulating path having a predeterminedradius with its center coincident with the axis of the drum asillustrated by the letter P in FIGS. 2 and 4.

In the condition of operation for effecting either single or multipleimage transfer with the solenoid SOL-3 energized to move the linkage toits position shown in FIG. 2, the cam follower 122 (see dotted position)in its revolution along the path P will engage the inner edge of thelink 116 at a point to the left of the shaft 117 which is in the path ofmovement of the follower for forcing the rod 1 11 inwardly. The followermakes contact with the adjacent end of the detent 121 which slows downradial movement of the rod 111 as it slides along the curve of thedetent. Without this detent upon striking the edge of the link 116, therod 111 would be propelled inwardly at too great a speed for thestructural parts of the drum. The resultant movement of the rod 111toward the axis of the drum is in opposition to the force provided bythe spring 108 upon the shaft 98. The opening 112 is of a sizesufiicient to permit this limited movement of the rod 111 relativethereto. This slight inward movement of the rod 111 will produce slightrotation of the shaft 98 and consequently will produce slight onwardradial movement of the registration elements 95 at the same time thatthe leading edge of a sheet of paper reaches these elements forregistration thereby (see FIG. 5). At the same time, the gripper fingers105 are rotated slightly out of the way to pen'nit sheet registration.Immediately after registration, the solenoid SOL-3 is deenergized formultiple image transfer to allow the linkage to assume the positionshown in FIG. 4 by virtue of the solenoid spring, and to allow thespring 108 to rotate the shaft 98 back to its original position. Thismovement produces outward movement of the rod 111 as it continues itsrevolving motion and out of the inner edge of the link I 16. With theshaft 98 moved to its original position, it allows the registrationelements 95 to assume their initial inactive condition and the fingers105 to grip the leading edge of the sheet material thereby permittingtransport and support of the sheet around the drum 20 (see FIG. 6 forthis completed action). As the drum 20 rotates, it carries the leadingedge of the sheet and the remaining portion thereof into the transferstation C to effect developed image transfer thereon. As the camfollower 122 continues its revolving movement and with the solenoidSOL-3 energized for single transfer, the follower engages the inner edgeof the link 113 at the leading end of the detent 120 and the rod 111 isdriven inwardly again in a softened action as provided by the detent.The position of the link 113 is such that this inward movement of therod 111 is greater than its inward movement provided by the detent 121.This action again rotates the shaft 98 against the spring force of thespring 108 except that the rotation is slightly larger than the initialrotation when the leading edge of a sheet was being registered. Thisadditional rotation causes movement of the gripper fingers 105 out ofcontact with the leading edge of the sheet and additional clearancetherefrom, and permits the projections 97 of the registration elements95 to move the leading edge away from the periphery of the drum. Aslight additional rotation of the drum will transport the leading edgeof a sheet over the leading points of fixed stripout fingers 130 (seeFIG. 7) and thereby remove the sheet from the drum as continued rotationthereof is made. As shown in FIG. 7, when the projections 97 have beenmoved to their outermost .position for the stripout mode of operation toseparate the leading edge of thesheet S from the drum, the leadingpoints of the stripout fingers 130 are adapted to enter slightly belowthe surface of tee projections upon which the leading edge of the sheetS is placed.

1 In operation just prior to a sheet being fed to the drum 20, thelinkage system comprising the links 113, and 116 are arranged as shownin FIG. 4 wherein the detents 1 20 and 121 are positioned so that thecam follower 122 will not coact with either during a completerevolution. In the event that only one transfer is to be made per copy,say when black and white copies are being made, upon a sheet S being fedby the feeder 21, the solenoid SOL-3 is energized to bring the inneredge of the link 116 into the path of the follower 122. After theleading edge of the sheet is registered and gripped, the solenoidremains energized so that the follower may engage the detent in order toproduce sheet stripout. In the event a threecolor series of images havebeen produced and three transfers on the same sheet are to beaccomplished, after the solenoid is energized to register and grip asheet of support material, it is quickly deenergized, before thefollower 122 can reach the link 113. In this event, the sheet cannot bestripped off the drum 20 as the camming surface of the detent 120 isheld away from the path of movement of the follower and the sheet willremain on the drum until three image transfers have been completed.After the last transfer and when the follower 122 has passed the detent121, the solenoid SOL-3 is again energized to position the linkage asshown in FIG. 2 in order to permit the follower to engage the inner edgeof the link 113. As previously described, upon this occurrence, thesheet S will be stripped off the transfer drum as it continues itsrotation. In summary, when the solenoid SOL-3 is energized. both cammingdetents 120, 121 are actuated into the path of movement P of thefollower 122. When deenergized both detents are actuated out of the pathof the follower. For single image transfer copies, after registration,the solenoid remains energized. For multiple image transfer copies,after registration, the solenoid is deenergized and remains so untilstripout.

For automatic operation, another sheet S of paper fed toward the drum bythe paper sheet feed mechanism 21 will be registered and gripped by theelements 95 and 105 as these elements continue around to the paperregister position of the drum 20. The paper feed mechanism working inautomatic conjunction with the transfer drum registration and grippingmechanisms feed individual sheets of paper into pinch rollers (seeFIG. 1) which are arranged to feed the leading edge of the sheet at agreater speed than the circumferential speed of the drum 20 in order topermit the leading edge to contact the registration elements 95.

While the invention has been described with reference to the structuredisclosed herein, it is not confined to the details set forth; but isintended to cover such modifications, or changes as may come within thescope of the following claims.

What is claimed is:

l. A transfer apparatus for use in a multicolor printing machine havingmeans for producing a series of one or a plurality of transferableimages of an original to be copied onto a printing member,

support means for supporting a sheet of transfer material and moving thesame in a recirculating path into contact with the member, said supportmeans including means for holding the sheet thereon and releasing thesame to permit removal therefrom, and

means associated with the support means for controlling the releasing inaccordance with a predetermined number of images of the original beingproduced.

2. A transfer apparatus for use in a multicolor printing machine havingmeans for producing a series of one or a plurality of transferableimages of an original to be copied onto a printing member,

support means for supporting a sheet of transfer material and'movingthe. same in a recirculating path into contact with the member, saidsupport means including means for gripping the transfer material forholding the same thereon and means for releasing the sheet to permitremoval therefrom, and

means associated with the support means for controlling activation ofthe releasing means in accordance with a predetermined number of imagesof the original being produced. 3. A transfer apparatus for use in amulticolor printing machine having means for producing a series of oneor a plurality of transferable images of an original to be copied onto aprinting member,

support means for supporting a sheet of transfer material and moving thesame in a recirculating path into contact with the member, said supportmeans including means for registering and gripping the transfer materialfor holding the same thereon in one mode of operation and means forreleasing the sheet to pen-nit removal therefrom in another mode ofoperation, and 7 means associated with the support means for placingsaid registering and gripping means in said one mode of operation inaccordance with the time sequence of production of the firsttransferable image of the original.

4. A transfer apparatus for use in a multicolor printing machine havingmeans for producing a series of one or a plurality of transferableimages of an original to be copied onto a printing member,

support means for supporting a sheet of transfer material and moving thesame in a recirculating path into contact with the member, said supportmeans including means for registering and gripping the transfer materialfor holding the same thereon in one mode of operation and means forreleasing the sheet to permit removal therefrom in another mode ofoperation, and

means associated with the support means for placing said registering andgripping means in said one mode of operation in accordance with the timesequence of production of the first transferable image of the originaland to place said release means in said other mode of operation inaccordance with a predetermined number of images of the original beingproduced.

5. A transfer apparatus operable in a multicolor printing machine havingmeans for producing a series of one of a plurality of transferableimages of an original to be copied onto a printing member,

a rotatable drum for supporting a sheet of transfer material and movingthe same in a recirculating path into contact with the member, said drumincluding means for registering and holding the transfer materialthereon,

means for normally maintaining said drum out of contact with theprinting means,

force-generating means associated with said last-named means forovercoming its nonnal effect on the drum when said force means isactivated, and

means associated with the force-generating means for ac-

1. A transfer apparatus for use in a multicolor printing machine having means for producing a series of one or a plurality of transferable images of an original to be copied onto a printing member, support means for supporting a sheet of transfer material and moving the same in a recirculating path into contact with the member, said support means including means for holding the sheet thereon and releasing the same to permit removal therefrom, and means associated with the support means for controlling the releasing in accordance with a predetermined number of images of the original being produced.
 2. A transfer apparatus for use in a multicolor printing machine having means for producing a series of one or a plurality of transferable images of an original to be copied onto a printing member, support means for supporting a sheet of transfer material and moving the same in a recirculating path into contact with the member, said support means including means for gripping the transfer material for holding the same thereon and means for releasing the sheet to permit removal therefrom, and means associated with the support means for controlling activation of the releasing means in accordance with a predetermined number of images of the original being produced.
 3. A transfer apparatus for use in a multicolor printing machine having means for producing a series of one or a plurality of transferable images of an original to be copied onto a printing member, support means for supporting a sheet of transfer material and moving the same in a recirculating path into contact with the member, said support means including means for registering and gripping the transfer material for holding the same thereon in one mode of operation and means for releasing the sheet to permit removal therefrom in another mode of operation, and means associated with the support means for placing said registering and gripping means in said one mode of operation in accordance with the time sequence of production of the first transferable image of the original.
 4. A transfer apparatus for use in a multicolor printing machine having means for producing a series of one or a plurality of transferable images of an original to be copied onto a printing member, support means for supporting a sheet of transfer material and moving the same in a recirculating path into contact with the member, said support means including means for registering and gripping the transfer material for holding tHe same thereon in one mode of operation and means for releasing the sheet to permit removal therefrom in another mode of operation, and means associated with the support means for placing said registering and gripping means in said one mode of operation in accordance with the time sequence of production of the first transferable image of the original and to place said release means in said other mode of operation in accordance with a predetermined number of images of the original being produced.
 5. A transfer apparatus operable in a multicolor printing machine having means for producing a series of one of a plurality of transferable images of an original to be copied onto a printing member, a rotatable drum for supporting a sheet of transfer material and moving the same in a recirculating path into contact with the member, said drum including means for registering and holding the transfer material thereon, means for normally maintaining said drum out of contact with the printing means, force-generating means associated with said last-named means for overcoming its normal effect on the drum when said force means is activated, and means associated with the force-generating means for activating the same when the latter is in condition for operation in the machine. 